I would say that a significant change affecting the natural environment and biodiversity could be the cultivation of corn and beans in mesoamerica which probably required the clearing of some land for the purpose. In populous societies such as the Aztecs the amount of cultivation would have been significant to feed a large population. In more recent times, the buffalo hunt of the First Nations and metis people in what is now Canada as long as it was carried out on a small scale for food and clothing was sustainable but once rifles were introduced and hides were sought and also due to a deliberate policy of extermination by the US military to destroy the independence of the First Nations and force them onto reservations, the bison were almost exterminated. In the 16th century, it was estimated that there were 25-30 million buffalo which is one of the largest populations of mammals recorded in the world. It is believed that the First Nations deliberately burned areas of the Great Plains to foster grasslands for the buffalo feed.